Discussion
Calculate the pH of 0.001 M barium hydroxide, assuming that it is completely ionized. Among the following, choose the correct answer.
Answer: B
The pH is 11.3.
Barium hydroxide is a strong base giving two hydroxide ions per formula unit: \(\text{Ba(OH)}_{2} \rightarrow \text{Ba}^{2+} + 2\text{OH}^{-}\).
\[ \begin{aligned} [\text{OH}^{-}] &= 2 \times 0.001 = 0.002\ \text{M} \\ \text{pOH} &= -\log(2 \times 10^{-3}) = 2.70 \\ \text{pH} &= 14 - 2.70 = 11.30 \end{aligned} \]
11.0 is what you get by forgetting that each Ba(OH)2 gives two OH- ions. 12.0 and 12.5 would need ten or more times the hydroxide concentration.
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